By NATHANIEL POPPER

February 19, 2014

The new financial index takes its name from the Winklevoss brothers, famous for their legal battle with the Facebook founder, Mark Zuckerberg. The Winkdex was released publicly on Wednesday and provides a regularly updated figure for the price of Bitcoin, the virtual currency that has risen in popularity over the last year.

The new filing shows that the Winklevoss Bitcoin Trust is moving closer to regulatory approval despite skepticism in some investor circles. The brothers are now hoping to start the fund later this year, making it the first Bitcoin E.T.F.

“We’ve been very encouraged with how responsive and deferential the S.E.C. has been to the application,” Cameron Winklevoss said.

The brothers and their company, Math-Based Asset Services, are being represented by lawyers at Katten Muchin Rosenman who have helped shepherd some of the most popular E.T.F.’s through the regulatory process.

The Winkelvoss Bitcoin Trust is set to be traded on public stock exchanges. The fund will work with other financial firms to buy and sell Bitcoin each day to remain in line with the number of outstanding shares of the E.T.F. The so-called net asset value of the fund will be adjusted at the close of trading each day, based on the value of the Winkdex.

The brothers first filed for the trust last July, soon after publicly disclosing their own sizable Bitcoin holdings. The brothers have also invested in several virtual currency start-ups. Their investments recently came under scrutiny after the founder of a company in which they invested, BitInstant, was arrested and charged with money laundering. The brothers said they were passive investors in the company.

The E.T.F. aims to provide an easy way for investors to bet on the future price movement of Bitcoin, which has gone through several volatile swings. Investors, though, will pay for the work that the Winklevosses’ company will do to maintain and secure the Bitcoin held by the E.T.F. The size of the management fee has not yet been specified.

There is already one investment fund, the Bitcoin Investment Trust, that allows Americans to bet on movements in Bitcoin’s price. That fund has $50.4 million under management, but it is available only to wealthier, accredited investors, and is not publicly traded.

The Winkdex will compete with a growing number of companies providing data on the virtual currency industry. The most popular index for the price of a Bitcoin is operated by CoinDesk, a news and information website.

CoinDesk’s Bitcoin Price Index is compiled using prices from two virtual currency exchanges. Until last week it also used the price from a third, Mt. Gox, but that was removed from the index after the exchange suspended customer withdrawals.

The Winkdex will use data from seven exchanges and weight the prices based on the volume of trading on each exchange. Early Wednesday afternoon, the Winkdex stood at $627, up 0.7 percent from a day earlier.